I. Field of the Invention
The present invention relates generally to the use of ozone as a bactericide, and more particularly to the use of ozone in inhibiting the formation of a biofilm on the interior surfaces of waste water lift stations, headworks, treatment facilities and the like to prevent erosion.
II. Description of Prior Art
Ozone is well known for its ability to destroy odors, especially those generated by sewage treatment facilities, distilleries, paper mills, and many other industrial processes, because it is highly reactive with most elements. The more common odors which must be controlled are those caused by organic nitrogen- and sulfur-containing substances, particularly skatole, methyl disulfide, hydrogen sulfide, dimethyl sulfide, methyl mercaptan, putrescine, and cadaverine. The reaction between effective amounts of ozone and these noxious gases substantially reduces the objectionable qualities of the surrounding air. Ozone is also known to be an effective bactericide, capable of killing most types of bacteria present in waste water treatment facilities.
Sewer lift stations and treatment facilities are often the source of such malodorous gases, because they serve as a local repository of sewage and other waste which is produced from the surrounding community. These lift stations collect sewage and waste water from a multitude of sources into a large holding tank, and a lift pump delivers the waste to a higher level so that it can flow into subsequent lift stations or to an appropriate waste water treatment facility. Since the lift pump is designed not to operate until the level in the holding tank reaches a predetermined level, the waste in the lift station may become very septic over a period of time. This condition has previously been thought totally responsible for the noxious odors which emanate from the lift stations.
Nor is this problem limited to lift stations. Other areas of waste water treatment facilities suffer from similar problems, most notably the headworks to waste water treatment facilities. Upon exiting the collection system and entering the treatment facilities proper, the headworks constitute the first device or group of devices that the waste water encounters. The head works typically include at least one of such devices as bar screens, grit chambers, flow measurement devices and flow equalization devices. Devices positioned prior to the treatment stages of the waste water facility are generally considered to be within the definition of headworks and are sometimes referred to as the pretreatment section of the treatment facility.
Lift stations and wet wells, particularly those constructed of concrete, also suffer from erosion of the roof and walls. Additionally, very often the structures containing the headworks are constructed of concrete and are adversely affected in a similar manner. Conventional thinking believes this erosion to be caused by the effects of hydrogen sulfide gas emitted by the septic waste. The erosion occurs primarily as a softening of the structure in various areas until the concrete "melts" away, leaving holes in the roof, especially in the corners. This erosion can also effect the sidewalls of headwork structures, regardless of whether these structures have a cover or a roof. Efforts to alleviate such erosion have focused on the elimination of hydrogen sulfide in the air space above the liquid under the assumption that it alone caused the formation of acids. Other explanations have theorized that differences in concrete composition and consistency render certain structures more vulnerable than others to such chemicals. Most importantly, this same type of erosion has been observed in varying degrees when the construction material was plastic, fiberglass, or concrete coated with a protective material supposedly resistant to hydrogen sulfide attack.
Various methods have been used in the prior art to cause ozone to react with these gases in an attempt to eliminate the objectionable odors and prevent further erosion, both problems being attributed to the presence of hydrogen sulfide. One such method involves the bubbling of ozone-enriched air into the liquid phase of the sewage or waste water, wherein the concentration of ozone is about 0.5% or greater by weight. This method is sometimes referred to as "wet oxidation" and requires very large dosages of ozone, typically in the range of a pound or more of ozone per day even in small applications. One disadvantage is that such high concentrations result in substantial equipment and operating costs. Another disadvantage is that a substantial portion of unreacted ozone accumulates in the vapor over the liquid, resulting in high levels of ozone which can cause excessive corrosion to the internal structures of the lift station and may even be released to the atmosphere in large amounts.
What is needed is a method for simultaneously destroying noxious odors and preventing erosion of the lift station or headworks interior by focusing on the real cause of erosion, namely the formation of biofilm on the roof and walls of the enclosure. In order to solve both these problems, as well as minimize the escape of unreacted ozone, a balance must be sought between the concentration of ozone in the air, the volume of ozone-enriched air administered into the enclosure, and the means by which the ozonated air is directed into the vapor space above the liquid. Once this is accomplished, erosion and noxious odors can successfully be eliminated from lift stations, headworks and related waste water treatment structures to a degree heretofore unknown in the prior art.